Two Popular Types of CTP Plates
The structure of waterless printing plates consists of aluminum plate base, photosensitive resin layer and silicone rubber layer. When exposed, the silicone rubber layer that sees light reacts, and the silicone rubber layer is removed by the developer. The part that does not see light forms the blank part of the printing plate, forming a negative plate.
The image part of the negative type waterless plate is slightly concave, and the ink is not easy to spread after inking. The silicone rubber layer in the blank part has a repelling effect on the ink. Therefore, no wetting liquid is required during printing, thus avoiding many faults caused by the wetting liquid. The ink used in waterless offset printing has lower viscosity and adhesion than that of the common offset printing ink.
The main components are high-viscosity modified phenolic resin and high-boiling non-aromatic solvents. It is easy to decompose when heated. Therefore, the ambient temperature should be kept appropriate during printing.
Waterless offset printing has a small dot gain value, which can be controlled within 3%. It can use 200-500 lines/in fine screen lines, and can print high-resolution printed products. If combined with FM screening technology, it can print incomparable high-end and exquisite printed products.
Waterless offset printing removes the uncontrollable water, so there is no ink emulsification phenomenon, and the printed product has uniform ink color and high saturation. When using waterless offset printing, generally 5 sheets of paper are consumed for formal printing, with low paper consumption and high production efficiency. As an advanced printing technology, waterless offset printing may replace traditional water-based offset printing.
Since waterless printing does not use dampening solution, it will not produce emulsification of ink. However, since there is no wetting water to repair and clean the plate surface during the printing process, the plate surface is prone to smearing. For this reason, the printing pressure of waterless printing should be lower than that of PS plate printing.
At present, domestic single-layer thermal CTP plates are mainstream products in the printing industry and have a high market share. However, single-layer thermal CTP plates cannot meet the requirements for long printing runs and UV-resistant ink printing. Double layer hermal CTP plate not only retains the excellent printing performance of the traditional single-layer thermal CTP plate, but also can meet the printing needs of long printing runs and UV-resistant ink.
According to the properties of the double-layer thermal CTP plate, it is very important to control the coating quality of the double-layer coating of the thermal CTP plate in actual production. In particular, the quality of the coating on the upper photosensitive layer directly affects the photosensitive performance of the printing plate.
The support body of the double layer thermal CTP plate is a sand-grained hydrophilic layer aluminum plate that has been treated with excellent technology. The photosensitive layer (lower layer) is a resin layer that is resistant to printing and UV ink, and the photosensitive layer (upper layer) is an alkali-resistant heat-sensitive layer. The infrared absorbing dye of the thermosensitive layer accepts infrared light, converts the light energy into heat energy, and transfers the energy to the acid-generating source.
The acid-generating source is decomposed by heat to produce protons H+. Under the action of heat, the phenolic resin decomposes to form a body structure dissolved in the resin. After alkaline water development, the exposed part of the resin layer is removed to form a blank hydrophilic layer, and the unexposed part forms an ink-philic pattern.
